Primarily, it is to avoid allegations of plagiarism and academic misconduct.
Secondarily, citing sources allows the reader to identify the sources that you relied on for your research.
It's easy: whenever you paraphrase the ideas of others, whenever you use a direct quotation, or whenever you cite a fact that isn't common knowledge, you need to cite your original sources, whether they are books, articles, or web site.
The keys to successfully citing your sources in APA Style are:
1. Determine if the report was written by an individual (analyst).
2. Here are suggested APA Style citations for reports from Mintel Academic and IBISWorld, where the analyst is named as the author of the report.